The present invention relates to a contacting and heating fixing apparatus, and more specifically, to a fixing apparatus in which an image formed of thermoplastic powder (hereinafter referred to as the toner) may permanently be adhered to a support body by heat and pressure.
Conventional fixing apparatus heretofore known has been designed so that a desired pressure is applied between two heated rolls to allow a recording medium having an unfixed toner image therebetween, whereby fixing is effected. This apparatus affords advantages over other types of fixing apparatus in that it requires less electric power and has less possibility of danger due to a fire break-out resulting from jamming of paper in a fixing station. In this fixing apparatus, the heating roll (hereinafter referred to as the first roll) has its surface coated with a heat-resistant parting material such as tetrafluoroethylene (Trade Name: Teflon) whereas the pressure roll (hereinafter referred to as the second roll) comprises silicone rubber or the like coated with fluoroethylene-propylene.
According to the fixing apparatus with the first roll noted above used, in order to prevent a viscous material such as toners from being adhered to the surface of the first roll (hereinafter referred to as the offset phenomenon), a method has been proposed in which offset phenomenon inhibitor liquid such as silicone oil is continuously coated on the first roll.
In the case of using tetrafluoroethylene as a heat-resistant parting coating for the first roll, the thickness thereof is usually from10 .mu. to 200 .mu. and the surface hardness thereof is relatively high because the parting coating is on a metal core. While the tetrafluoroethylene is preferable in terms of strength of the surface coating, it has suffered from drawbacks such that the image is smashed and toner particles in fog portions are also smashed, resulting in the poor copy quality, since such hard roll is brought into contact with the image to be fixed at the time of fixing while being applied with pressure. In order to overcome the drawbacks noted above, there has recently been developed technologies in which silicone rubber having a flexibility is used as a coating on the first roll. However, even if RTV (room temperature vulcanized type) silicone rubber, which has generally been admitted to have a good parting property, should be used, the service life thereof with respect to the parting property would be short unless the offset inhibitor liquid is supplied. Further, when the silicone oil is supplied as the offset inhibitor liquid, the parting property may be increased, but the rubber itself is swelled by the presence of oil to decrease strength and as a consequence, the surface of adhesion between the silicone rubber and the metal core may be destroyed. In this case also, it is difficult to maintain a long service life. In order to solve these problems noted above, there have been proposed, for example, a method for pre-swelling silicone rubber with silicone oil, and particularly, RTV silicone rubber or the like containing a great quantity of silicone contents whose low molecular weight is analogous to silicone oil. In any of these proposals, the parting property comes to its life at the time when oil contents initially held have been run out to thereby extend the life. But it was not a satisfactory means of settling the problems.
In FIG. 1 there is shown a conventional contacting and heating fixing apparatus which comprises a first roll a having a heat-resistant parting outer layer d externally coated on a metal core c encasing therein a heating element b, and a second roll e having a layer h of fluoroethylene propylene externally coated on a silicone rubber layer g round a core f. The first roll a and the second roll e are cooperated with each other by a mechanism not shown to apply pressure to a nip portion thereby through which a support body j of toner i travels. A supply member k supplies an offset phenomenon inhibitor liquid m to the first roll a through an intermediate supply member l and also serves as a cleaning member for cleaning the first roll a. The offset phenomenon inhibitor liquid m within a container o is supplied by a supply roll n for supplying the offset phenomenon inhibitor liquid to the intermediate supply member l. The reference character p designates a weight. A cleaning member q and a support member r thereof are placed in contact with the second roll e.
In the conventional contacting, heating and fixing apparatus, wherein the heat-resistant parting outer layer d of the first roll comprises silicone rubber and the offset inhibitor liquid m silicone oil, when the oil is supplied, the silicone rubber is swelled with silicone oil to decrease the strength, and particularly, the surface of adhesion between the silicone rubber and the first roll core easily comes off.